Although three generations of Jud Canovas have distinguished themselves in service to their country, from Bull Run to World War I, the line of military Canovas seems to have ended when a daughter, Judy, is born instead of a fourth Jud. On the same night, lightning in the town square destroys the statue of Jud Canova I, and over the years, Judy's recurring mishaps delay Gramps Canova's efforts to restore it, until finally his nemesis, Col. Mayfield, convinces the town council to put a Mayfield hero on the empty pedestal. Despite the Mayfield-Canova feud, the grown-up Judy develops a crush on young Lt. Tom Mayfield, and when Tom says he needs to ask her about a hayride, she joyously assumes he wants to ask her for a date. Needing a dress for the occasion, Judy visits the town's only dress shop which is run by the sophisticated Doris Vail, who is Judy's rival for Tom's affection. When the unfashionable Judy chooses an outfit that is hanging in the shop's unfinished window display, Doris points out that it is a special outfit, only available from a woman down the street. After introducing herself to the woman, a WAC recruiting sergeant, Judy learns that the dress she admires is really a WAC uniform. Meanwhile, two men identifying themselves as Prentice and Redington of International Amalgamated arrive in town and want to hire Tom for a project. As a military officer on active duty, he rejects their offer, leaving them to report their failure to their boss, who then decides to handle the matter himself. As Judy is leaving the recruiting sergeant, Tom sees her and states how proud he is that she has joined up, and then asks if he can borrow her family's wagon to use for the hayride. Broken-hearted that she was not asked for a date, Judy decides to attend the hayride on her own, and that evening, she and Doris end up sitting on the wagon with Tom, who is oblivious to their rivalry. When Doris teases Judy about mistaking a WAC uniform for a chic dress, the embarrassed Judy explains that she was set straight by the recruiting sergeant, but enlisted after Tom expressed pride in her. In the morning, when Judy reports at the train station with the other new recruits, Doris is among them, having enlisted with the hopes of also winning Tom's approval. For the naive Judy, basic training is difficult, as Doris' incessant tricks often get her into trouble. During compass training, Doris alters the directions on Judy's instruction sheet, causing her to wander into an area where live ammunition is being used. Mistaken for one of the men, she is dragged through their maneuvers, and after shaking them off, is almost arrested for trespassing in a top secret area. Fortunately, Tom recognizes her, and tells her about the guided missile homing device they are testing. Later, when the women complete their training, both Judy and Doris ask to be assigned to Ordnance to be near Tom. Shortly after reporting for duty, they are confronted by a general who wants data about the missiles. However, when he says his name is Mayfield and describes the Canovas as "fine people," Judy is certain that he is a phony. Working with the bogus general are Prentice and Redington, and the three spies escape with the homing device for the secret missile, a black box. By chasing them in an Army jeep, Judy catches up and rides off with the black box, but meanwhile, the rocket has been launched as part of a demonstration for top Army officials, and the box is its target. Judy unwittingly toggles the switch on the box, causing the rocket to circle above, but when the spies get too close to her, toggles it back, letting the low-flying rocket scatter them. The chase continues on foot after Judy's jeep gets stuck. Using the box as a blunt object, she knocks out one of the men, and even disables the second spy. As she is wrestling with the third, Doris and Tom, both of whom are impressed, arrive with help. Later, for her service in apprehending the spies, Judy is awarded a medal during a hometown ceremony in which the statues of Jud Canova I and Major Mayfield are unveiled together in the town square. After the ceremony, Judy joins a parade of her fellow WACs, as they all march away.